Matching pairs based on criteria

Hi all,

On the attached spreadsheet is 28 rows of data, across columns A-M (with F to I hidden)

The data shown are pairs, based on their location and the times. The cell in column M is highlighted when there is a location and time match.

At times I can work with 000's of rows of data and then I need to number the pairs in column D, as shown.

A pair would be worked out based on column M being highlighted and the times in column C for the rows are within 10 minutes of a different coloured call (as shown by column A).

I have started numbering the instances to show an example, but for 20,000 rows where there could be 9,000 instances it is hard to do manually.

Any ideas how to automate the pairing?